One form of technology currently available for fire protection glazing employs two or more panes of glazing materials separated by means of a spacer around the perimeter of the panes. The cavity between the glazing panels is entirely filled with a transparent gel, that stays transparent at ambient temperature. A primer for better adherence of the gel layer to the inside of the glazing panes is applied to the inside of the glazing panels before the cavity is filled. Ultimately the gel tends to harden after a certain time and in the process may discolor or develop discontinuities or otherwise mar the appearance of glazing panels.
A major disadvantage of this prior art fire protection glazing is a relatively great weight commonly on the order of approximately 12 pounds per square foot. The weight is due to the thickness of the gel layer and to the weight of the glazing panels. The weight of the fire protection glazing complicates the many difficulties in handling and transportation of the panels or installation of panels at the construction site. Therefore the possibility of breakage and damage is very high during manual transportation on the construction site and during loading onto and unloading from trucks.
Greater weight also requires stronger and heavier structure to hold the glazing in place after installation, and often involves some form of proprietary framing system.
An additional disadvantage is the relatively low light transmission through the glazing material. Up to 20% loss of light transmission has been observed. The pressure created in filling the cavity between the glass panels also creates a deformation of the gel. The resulting optical refraction and reflection creates distortion of the view through the glazing panel.
Furthermore, the filling of the cavity between the glass panels requires an enormous amount of attention and precision. If the cavity is not filled properly, or the adhesion between the applied primer and the gel is not exact, air bubbles in the gel will appear. Such air bubbles distort visibility through the glazing panel.
This prior art type of fire protection glazing also has a high degree of sensitivity to high and low temperatures. Because of this sensitivity, an installation of the glazing in environments which will be subjected to temperatures below approximately -18.degree. Celsius (5.degree. F.) and above +60.degree. Celsius (140.degree. F.) is not recommended. The fire protection gel will crystallize at temperatures lower than -18.degree. C. and therefore lose its transparency. At temperatures above +60.degree. C. the possibility exists of a premature reaction turning of the gel layer opaque. Such premature reaction of the fire protection gel can even be observed in panels directly exposed to sun light. Where an exterior application requires an installation of this type of glazing material, an additional pane of insulation glass has to be installed in front of the fire protection glazing. The additional glass not only increases the cost and the weight of the total structure but also lowers the light transmission through the glazing material.
Another currently available technology is the installation of a thin, transparent fire protection film between two or more glazing panels in a sandwich or laminated structure. The fire protection rating is determined by the number of glass panels aligned in series. In some instances a dead air space or vacuum between the glass panels is required to achieve a high fire resistancy. Such a laminated construction does not provide a vacuum or a dead air space within the individual panels so that multiple panels must be used in series.
This technology also produces a weight of approximately 12 pounds per square foot and the same disadvantage concerned with weight as the previously discussed prior art structure.
An additional disadvantage is that the additional layer may reduce the light transmission as much as 35%.
The danger of breakage due to the multiple glazing panels is apparent. The handling and transportation therefore requires maximum attention to reduce the amount of loss both in the manufacturing process and on the construction site before and during installation. This hazard is further increased because the product is often installed by unqualified workmen who do not fully understand the need to take special precautions against damage or breakage.
Again this sandwich construction often has sensitivity to temperatures below -18.degree. C. and above +60.degree. C.